Among conventional semiconductor devices provided with the first electronic element and the second electronic element that has larger current passed therethrough as compared with the first electronic element to generate large heat is, for example, a semiconductor device having a control element such as microcomputer as the first electronic element and having a power element controlled by the control element such as power MOS element and IGBT as the second electronic element.
The semiconductor device provided with these control element and power element is used for driving an actuator, for example, a motor.
The application of a semiconductor device provided with the control element and the power element like this to a HIC (hybrid integrated circuit) for driving a driving motor of a power window having a JAM preventing function has been conventionally proposed, for example, in Japanese Patent Application Publication No. H07-67293.
Further, a method of driving the power window having a JAM preventing function like this is described in, for example, Japanese Patent Application Publications No. H07-113376 and No. H07-76973.
Here, in the conventional semiconductor device described above, large heat is transmitted to the control element via a wiring board easily transmitting heat from the power element that has larger current passed therethrough as compared with the control element to generate large heat, whereby the control element is apt to be affected by the heat.
The control element is limited in operating-temperature and usually has a lower operating temperature because it has delicate construction as compared with the power element. Hence, it is important to prevent the effect of heat from the power element as described above.
In simple terms, it is recommendable to increase the distance between the control element and the power element on the wiring board on which the control element and the power element are mounted, but in this case, the device results in increasing in size, which is not desirable.
The above-described problem is thought to be common to a semiconductor device having the first electronic element and the second electronic element that has larger current passed therethrough as compared with the first element to generate large heat. That is, in the semiconductor device like this, it can be an important problem to prevent heat transfer from the second electronic element to the first electronic element.
Further, an electronic device made by mounting a heating element and a temperature-limited element on a heat sink and then by molding them in such a manner as to wrap them by a molding resin is also disclosed in Japanese Patent Application Publication No. H07-67293.
The electronic device of this kind is usually made by mounting a heating element of an electronic element, which generates heat under large operating current passed therethrough, and a temperature-limited element of an electronic element, which is limited in operating temperature, on a heat sink and then by molding them by a molding resin.
Here, the heating element is an electronic element that has a larger current passed therethrough as compared with the temperature-limited element to generate large heat. Among the temperature-limited elements is, for example, a control element such as microcomputer. Among the heating elements is a power element, which is controlled by the control element, such as power MOS element and IGBT or a resistor.
The electronic device provided with the control element and the power element like this is applied to, for example, a HIC (hybrid integrated circuit) for driving an actuator such as motor. To be specific, the application of the electronic device to the HIC for driving a driving motor of a power window has been proposed in Japanese Patent Application Publication No. H07-67293, although it is not intended to limit the application of the electronic device to this.
However, in the conventional electronic device described above, large heat is transmitted to a temperature-limited element from a heating element that is larger in the amount of current and in the amount heat generation than the temperature-limited element via a heat sink easily transmitting heat, whereby the temperature-limited element is susceptible to the heat.
The temperature-limited element is limited in operating temperature and usually has a low operating temperature because it has finer construction than the heating element such as power element. Hence, as described above, it is important to prevent the effect of heat from the heating element.
In this respect, to be simple, it can be thought to increase the distance between the temperature-limited element and the heating element on the heat sink on which the temperature-limited element and the heating element are mounted. However, this results in increasing the size of the device, which is not preferable.
Further, in the related art, as an electronic device provided with the control part and the driving part of this kind has been proposed, for example, an electronic device provided with a control part mainly including control elements such as microcomputer and control IC and a driving part mainly including driving elements of power elements such as power MOS elements and IGBT.
The electronic device like this is applied to a HIC (hybrid integrated circuit) for driving and controlling an actuator such as motor. To be specific, an application of electronic device to a HIC for driving a driving motor of a power window has been conventionally proposed in, for example, Japanese Patent Application Publication No. H07-67293.
In recent years, automobiles have been more sophisticated in functionality and higher in grade and various actuators have been used with this trend. For this reason, electronic devices necessary for controlling these actuators have been increased in number and the electronic devices themselves have been enlarged in size.
However, under these circumstances, when an electronic device is mounted in an actuator to make an integrated assembly, there is a tendency that the enlarged size of electronic device, as described above, increases space for mounting the electronic device in the actuator and makes it difficult to secure the space for mounting the electronic device. For this reason, an attempt to integrate the electronic device with the actuator results in upsizing of the actuator.
Further, an electronic device provided with a plurality of connection terminals that are connected to bonding wires and are connected to external parts by welding has been conventionally known. To be more specific, a mold igniter is known as an electronic device like this.
The electronic device like this commonly has a construction in which, for example, a circuit board or an IC chip is electrically connected to connection terminals via bonding wires made of Al (aluminum) thick wires.
Here, since bonding wires need to respond to large current used for power MOS elements and the like, the Al thick wires are used as the bonding wires and Al thick wires having a wire diameter of, for example, approximately 250 μm to 500 μm are used.
Further, connection terminals made by nonelectrolytically plating a lead frame made of Cu (copper), or Fe (iron) with Ni are used as the connection terminals. With this, the connection terminals can be suitably connected to external parts by welding.
Usually, in this kind of electronic device, the connection between the connection terminals, through which a large current is passed, and an external part, for example, an actuator is made by welding so as to secure the ease and reliability of connection.
In this regard, in the related art, a lead frame of a connection terminal has been proposed in which a nonelectrolytic Ni/Pd/Au film is formed in a bonding area and a soldering part to realize a connection terminal of excellent soldability and free of Pb. This is disclosed in, for example, Japanese Patent Application Publication No. 2003-23132. This connection terminal can be realized only for an Au bonding wire and is connected to an external part by soldering.
However, to achieve greater functionality, in an electronic device of this kind, the electronic device needs to be provided with control elements such as microcomputer and memory element. When the electronic device is provided with the control elements like this, the electronic device results in increasing connection terminals in number, that is, having multiple pins.
When the electronic device is required to have multiple pins, and when Al thick wires are used as bonding wires, the spaces between the connection terminals need to be elongated or the bonding parts of the connection terminals need to be enlarged in size, which leads to the increased size of the device and by extension to increased cost. Further, in the case of element that is small in size and needs many wire connections, it is difficult to make the wire connections by use of the Al thick wires.
To cope with this problem, it is thought that in place of the Al thick wires, for example, Au (gold) thin wires having a diameter of approximately 20 μm to 30 μm are used to solve the problem.
However, Au thin wire can not respond to large current. Further, Au thin wire also presents a problem that, usually, Au thin wire can not be bonded to connection terminal nonelectrolytically plated with Ni.
Here, when the surface of connection terminal is not nonelectrolytically plated with Ni but is electroplated with Ni and is further plated thereon with Ag, Au thin wire can be bonded to the surface plated with Ag.
This is a proven combination in a monolithic IC in which the surface of connection terminal is electroplated with Ni and then further electroplated with Ag. In this construction, Au wire can be easily bonded to the surface plated with Ag.
However, as described above, when the surface of connection terminal is not nonelectrolytically plated with Ni, weldability can not be secured in the connection between the connection terminal and the external part. Further, the bonding of Al wire to the connection terminal electroplated with Ni is difficult in securing flatness as compared with the bonding of Al wire to the connection terminal nonelectrolytically plated with Ni and hence can not be performed with ease.
Therefore, in the electronic device of this kind, it is essential that the surface of connection terminal is nonelectrolytically plated with Ni and this nonelectrolytic plating can not be omitted.
Further, an electronic device according to a conventional art includes a heat sink, electronic elements mounted on the top surface of the heat sink, a lead frame provided around the electronic elements, and molding resin that molds almost the whole device in such a way as to expose the bottom surface of the heat sink, and a method for manufacturing the electronic device.
To be specific, the electronic device of this kind is manufactured in the following manner: electronic elements are mounted on the top surface of a heat sink; a lead frame is provided around the electronic elements; and the lead frame is connected to the electronic elements.
In addition, the heat sink is bonded to the suspending leads of the lead frame. In this manner, an integrated part into which the heat sink, the electronic elements, and the lead frame are integrated is placed on the bottom mold of a mold and then a top mold is mated with the bottom mold. With this, the integrated part is placed in the cavity of the mold.
Molding resin is filled into the cavity to mold the heat sink, the electronic elements, and the lead frame by the molding resin so as to expose the bottom surface of the heat sink. In this manner, the electronic device is completed.
By the way, according to a conventional manufacturing method like this, a portion of top surface of the heat sink, that is, a portion of mounting surface where the electronic elements are mounted in the heat sink is pressed by the pressing portion of the mold.
For this reason, a portion pressed by the pressing portion of the mounting surface of the heat sink becomes dead space to limit space for mounting the electronic element. This prevents high package density and increases the size and cost of the device.
In this regard, it is also thought to press such a bonding portion of the heat sink and the suspending lead that is not related to space for mounting the electronic element in the heat sink. However, in this case, there is a possibility that the bonding portion is displaced by the pressing force to displace the lead frame with respect to the heat sink. Hence, in the conventional method, a portion of top surface of the heat sink is pressed by the pressing portion.
On the other hand, in a method for molding a resin-molded semiconductor device having a heat sink on the bottom surface of a die pad, a method has been proposed in which resin is molded while the bottom surface of a die pad is being fixed to the bottom mold by sucking from a suction hole formed in the bottom mold of the mold to prevent the resin fins on the bottom surface of the die pad. This is disclosed in, for example, Japanese Patent Application Publication No. H05-55280.
However, according to the method described above, a mold does not press the surface of a heat sink on which electronic elements are mounted and hence dead space is not provided. However, the method requires a manufacturing machine provided with a suction unit and hence raises a problem of upsizing of the machine and increasing cost.